You should put holes only in the bottom of the box for mounting. Then
leave a vent hole in the bottom for drainage of any condensation.

I have a couple of large electrical junction boxes with the lid and
gasket outside for cables. All entrances are from the bottom. No holes
to mount anything except in the bottom. Stays nice and dry.

73
Gary K4FMX

Keith Dutson wrote:

I need to weatherproof a relay box. Under test conditions it accumulated an
inch of water in the bottom over a six month period. What is a specific
brand of silicone sealant recommended? I understand the kind with vinegar
smell (acetic acid) will corrode electronics components in a sealed
environment. Also, is there a need to insert a desiccant in the box?

The box is NEMA industrial type, made of plastic with neoprene o-ring seal
on lid. However, there are many holes drilled for stainless hardware used
to mount the relay and connect wires to the exterior. The relay itself is
the open contact variety with self-cleaning contacts (hot switch 20 watts
RF), and supposedly impervious to damp conditions.